1. Field of the Invention
This invention relates to a device for determining the blood sedimentation rate by a change in the electrical or magnetic property measured as a function of time, which change is caused by the settling of the erythrocytes in the blood.
2. Description of the Prior Art
The invention is used in medical laboratories, in clinics and by practicing physicians. Although the determination of the blood sedimentation rate is a non-specific method and permits no differential-diagnostic statements, it is extremely well suited for a first clarification of a pathological pattern and for therapy control. In the measurement of the blood sedimentation rate, use is made of the fact that normally, the erythrocytes, after being mixed with sodium citrate, if indicated, to prevent the blood from coagulating, settle from the suspension at a definite rate. For comparison, reference values have been determined. In pathological cases, the erythrocytes agglomerate more, which causes the particles to settle faster. The sedimentation reactions can vary greatly here.
Two similar methods for determining the blood sedimentation rate reaction are generally known, namely, the method named after Westergren with a determination of the height of the boundary layer at definite times, and the method named after Linzenmeier with a determination of the time of sedimentation of the boundary layer by a defined height difference. The methods are described in detail in the basic medical literature.
In one known device of the type described (French Pat. No. 2.201.762), a high-frequency square-wave pulse current is introduced by means of two electrodes connected to the oscillator via the bottom of the test tube into the adjacent volume of liquid. The amplitude change of this square-wave due to the settling of the erythrocytes into the measurement volume and the changed conductivity thereof is measured. This purpose is served by a null indicator and an appropriate reference signal. This is followed by an amplitude/frequency conversion, pulse shaping, frequency division and adaption of the pulse sequence for the succeeding counter; and the indication can be made, of course, in a manner familiar to the physician, e.g., in values for the corresponding blood sedimentation rate. The measurement in the bottom zone can be falsified greatly by dirt. The measurement signal passes through a number of circuit components in series, so that errors resulting from null drift lead to further inaccuracies. The method of measurement covers a volume of liquid, i.e., the bottom region of the test tube, in which the measuring process can be completed very fast or the hematocrit value can be reached very quickly, whereas it is the comparison of the lowering of the boundary layer between the erythrocyte column and the plasma with reference values, that is of interest to the physician, as explained above.
In other known devices, an opto-electronic measuring arrangement is run up and down along the test tube (German Published Non-Prosecuted Application No. 2 353 272; German Utility Pat. No. 1 776 034). As is well known, mechanically moved parts are trouble-prone. The optical determination of the boundary layer is inaccurate because the latter is often not developed sharply enough. In the last-mentioned known case, however, an embodiment example is indicated, in which the light source required for the optoelectronic measurement and the photoelectric receiver can also be replaced by capacitor electrodes and a capacity measurement is to be made, as pure blood serum has a dielectric constant different from that of concentrated blood. However, it is not stated how the accurate measurement and further processing of the measured value are to be performed.
In measuring methods which operate with moving measuring devices, much time is required from the start of the measurement until a result is available. Assuming a mixture of blood with sodium citrate, a relatively flat curve is obtained for the sedimentation reaction, i.e., the function of the height of the erythrocyte column versus time. From the instant of filling up to a first point in time, the erythrocyte column is lowered slowly, due to the turbulence resulting from the filling operation. This is followed, with a gradual transition, of course, by an approximately linear region, in the center of which a second point in time can be defined. From a third point in time, there follows again a flatter region of the curve, as the packing density of the particles has become so great that it approaches the hematocrit value. According to empirical determinations, the interval from time 0 to the first point in time can be made on hour and the interval from the first to the second point in time, two hours. As the initial sedimentation rate, as described, is smaller than the sedimentation rate in the linear region and the occurring turbulence may be different and depends on further factors, there is a great spread in the so-called one-hour value. Now, it would make good sense to choose the time interval for the linear region, as this region has less interference; however, if the sedimentation is greatly accelerated, the hematocrit value can be reached substantially sooner, of course. In some cases, a planned interval of, say, two hours could be too short.
Methods are also known, in which capillary tubes or tubes provided with Heparin or another coagulation inhibitor are used in the blood sedimentation reaction (German Published Non-Prosecuted Application No. 2 137 622 and German Published Prosecuted Application No. 2 442 877). Common to both methods is the fact that dilution and prevention of the blood coagulation by liquid substances such as sodium citrate are unnecessary. In fact, using tubes coated with Heparin, for instance, simplifies the blood sedimentation determination considerably. Capillary blood can be used instead of veinous blood, and throw-away tubes can be used for mechanization. The time function of the height of the erythrocyte column has the same characteristic as the one described before, but is much more compressed in time. In particular, the time to the beginning of the linear region is substantially shorter.